They turn your phone into anything from a torch to a spirit-level. They have made billions for their creators. And they have changed the way millions of us work, rest and play.

Yet just five years ago this week, when Apple launched the App Store, most of us had not even heard of them.

Apps – short for applications – are tiny pieces of computer software that perform specific tasks on your smartphone, or tablets such as the iPad.

There are apps for booking taxis, checking the weather, monitoring your calorie intake, reading the news, ordering a meal or identifying a song on the radio.

There are games, translators, satnavs, ebook readers, sketchpads, expense calculators . . . and apps that let you make your photos look like they were taken in the 1970s.

When the App Store launched in July 2008, there were just 500 apps available, including app versions of popular websites eBay, Travelocity and Facebook. And they were downloaded 10 million times in the first weekend.

Today there are 900,000 apps which have been downloaded a total of 50 billion times.

Steve Furber, Professor of computer engineering at the University of Manchester, says: “Apple reinvented the mobile phone.

"The App Store was preceded by iTunes, the idea you could download music any time you wanted.

“Apple extended that so you could pick up functions for your smartphone instantly and cheaply.

“The App Store is also the source of updates for that software – so if you have a smartphone, the apps are constantly updated. Previously you had to download stuff on to your computer, install it and follow instructions on your screen.

“It all required a reasonable degree of confidence in the user. But with the App Store, it is instant gratification. You push the button, enter your password and the software is ready to go.

“The App Store has given us much more ready access to the information that we need. It has made so many aspects of life so much more efficient.”

The App Store is also responsible for helping bedroom computer geeks turn their ideas into multi-million pound fortunes.

Creating the app is just the start though. Apple experts assess every app before deciding whether it can be sold on the App Store.

It may see developers jumping through hoops but it has kept the service free of the pornography that plagues the internet.

And there are huge profits at stake if your app catches the world’s imagination.

Apple has paid out £6.7billion to developers, even though it takes a 30% cut of sales.

Instagram was developed by Kevin Systrom and Mike Krieger while they were students at Stanford University, California.

The app was launched in October 2010 and they sold their company in 2012 to Facebook for £670million.

Systrom said: “I figured we’d have 2,500 sign-ups on our first day. Instead we got 25,000 from all over the world. It was crazy.”

Since then, 16 billion photos have been shared on Instagram – 45 million images daily.

Loaded: 17-year-old Nick D'Aloisio (Photo: Getty)

Earlier this year, Wimbledon, South West London, schoolboy Nick D’Aloisio sold his app Summly to Internet giant Yahoo for an estimated £18million.

The 17-year-old created the app in his own bedroom just over a year ago to provide summaries of stories from news and other websites.

Addictive game Angry Birds is the most downloaded paid-for app of all time, created by Finnish games developers Rovio.

The game, where players use a slingshot to launch birds at their enemy pigs, may be annoyingly addictive but the company is said to be worth £5.5billion.

Facebook was the most popular free app for the smartphone, followed by Pandora, Instagram, YouTube and Skype.

Games Apps have created a generation of toddlers who are more tech-savvy than parents.

But the App Store is no longer the biggest in the world. Google Play is hotting up the competition with 975,000 apps available to download.

And android handsets have edged out the iPhone to become the UK’s top smartphone.

In 2012, 36.9% of smartphone users owned an android device using Google software compared with 28.5% using an iPhone, while 18.1% used a BlackBerry.

But as it celebrates its fifth birthday, nobody would deny that it was the App Store that changed how we use our phones for ever.